Roasting sulfide ores



May 5, 1953 w. KT I Ewls' RoAsTING SULFIDE oREs Filed June 2. l1947` H EAT Emu-Anaal HGPPEQ Vissen.

@im uP VESSEL.

GAS INLET "warren, I.L2ufi5 Jnventor Clttor'ne Stage. 'that the oxidation'of ithe-vaporizedsulfur from `the initialore is substantiallyisegregatediromthe Patented May 5, 1953 UNITED PATENT OFFICE Roe- SUNG SULFIDE omis Warren K. Lewis. Newton. Mass.. assigner to Standard Oil Development Company, a corporation of Delaware Application J .2, 1941,' ySerial u. 'I5-1,7480 s claims; (ci. 234-117) The present invention 41s directed to a method for roasting sulfide ores, particularlypyrltes. y

vIn the roasting of sulfide ores, of which pyrites is the most commonly employed, for :the produc,-

-tion of S02 for use as such or for conversionpto its salts, the principal objective is lto produce a gas substantially free lfrom S03, excess yoxygen and sulfur vapor. Sulfur vapor. if contained in the nal product, condenses on cooling surfaces when it is sought to liquefgy the S02 and inter-'- ieres with cooling. Excess oxygen oxidizes SQ:

-to S03 when the SO2 is dissolved in aqueous solution as such or in the formfof sulfites -or bysulltes. Hitherto diiculty has been encountered in Yachieving this objective.

'important beoause'the presence of residual sulfur in the cinder renders the latter unusable Lfor many purposes, for example, Yas chargeto anilon blast furnace or as a catalyst or catalyst hase. It is an additional objectoffthe present invention to insure substantially complete elimination 'of sulfur from the sulde ore.

Briefly, inthe method of the present invention, A

4the suliide ore is vprocessed-in finely divided form. Itis prei-erred that the ore Abe ground to asize such that substantially all oiit will pass through 1GO mesh screen. For vthe best Vperformance vthe ground ore should vinclude 'a Vwide range `0'f'vpa1-ticlge `sizes ranging upwardly from rabout$2.0microns t'o "about 100 mesh with a large proportion `ofgmaterial between about 200 vand 400 mesh.

in essencethe method ofthe present invention resides in the processing ofthe oreiinf'stageshe initial distillation andpartial oxdtionoccurring in a `first stage with the finely ground .Ore 1 8 fiuidized condition, the residualgpartially oxidized ore being further oxidized in asecondstage, again lin a fluidized condition so as to :bring the `sulfide ycontent down to a verylowlevel,fandtheresidual ore from this stage being-subjfectfedto a clean-.up It is a ieatur-e ofthe presentdnvention distillation step proper. Another feature-ofthe present linvention `is that -fsintering temperatures :are avoided at allpointss'wh'ere solidsare present.

. Other .fe-atureso the present i invention willlbe. `evidentrfrom the-followingfetailedfdescrlptionfof u depicted forvlllustrative purposes only.

theaccompanving drawing in which the single ligure is a front elevation in diagrammatic form of a plant suitable vfor the practice of the present invention.

rReferring to the drawing in detail, numeral I designates' a hopper lfor ground sulfide ore having a -drop leg 2 `which vdischarges into the bottom portion of a vessel y3 which may be termed a distillation zone. The drop leg is provided with a suitable feed .control valve 4 and may also be provided with suitable aeration jets so as to maintain the powdered material therein in an aerated condition.

The -vessel 3 is provided near its bottom, preierably below the point of entry of the drop leg `2, with a grid orgrate 5 below which is an inlet line 6 for air, pure oxygen, or oxygen-enriched gas. At its -upper end the vessel 3 is provided with an internal cyclone 1 yhaving a dip leg 3 which terminate's at a point in the reactor where the solid is present in the form of a dense suspension. To achieve such a suspension, the velocity of the gas introduced through line 5 through the vessel is vmaintained at a value between about 1/2 and 5 Ift./sei e,ond, preferably about l and 3 ft./second. At --velocities in thi-s range the powdered material exists in the form of a dense, uidized suspension having a denite upper level such as indicated by 9. By' dense is meant a suspension containing atleast 6% by volume of solid, and, preferably, "between l0 and 25% by volume of solid. The exact density of the suspension will depend on the rate of Ithe feed of the solid as well as on the velocity of the gas. With enough solid in the zone to provide a given density at a given velocity, this density can be maintained by feeding solid at the same rate at which it is withdrawn from the vessel.

Vessel 3 is also provided with a dense phase drawoff il) which inthe embodiment shown is in the form of ,a duct arranged along one .side of the vessel having its ppen upper end terminating at -about'thelevel desired for the vdense .phasein the "reactor so that solid material can overflow vfrom the dense phase into the drawoi. Suitable aerating jets I=I are -provided along the duct vill to mantainthe material therein in an aerated condition.

Vessel 3 is also provided with an internal coil sli! through ywhich may be circulated a cooling medium suitably selected with regard to the temperature vto 1bemaintained in the vessel 3. It will beunderstoodthat other forms of heat exchange videvicesfrmiybe employed and that a simple coilvis removed from the ore. shown, this vessel is filled withpacking 39 in the Vresting on a grate or grid 4I). loxidizing gas is fed into the bottom of y this ducting gas from the upper end of vessel 3 to an upper burning chamber 20. A supplermental`` supply of air or other oxygen-containing gas may be introduced into the system at this-'point 1 through line 2I. y l

The chamber 20 may assume any desired form and may be, as shown, filled with packinghl such as Raschig rings, ceramic balls, or the like,\

4 with oxidation of Fes occurs at or near the point oi.' distillation of the sulfur. The high heats of reaction cause high localized temperature, resulting in well recognized sintering difculties. The system of the present invention segregates final sulfur vapor oxidation from the distillation zone but furnishes the heat of distillation by partial 'combustion of sulfur vapor and of Fes in vessel 3. In the operation of the present invention, all distillable sulfur is removed from the solid in vessel 3. In order to insure this result enough 'air is fed upwardly through the vessel to burn resting on a grate or grid 23. It is preferred 'that f the gases entering chamber pass through a "mixing device 24 so as to insure thorough mixing fof the components.

f Combustion gas leaves the upper end of burning zone 2B through a line 25 which passes .through a heat exchanger 26 and thereafter 'connects with line I5 through valve 2l.

The fluidized solid leaving vessel 3 through duct I0 passes through a continuationl of this duct, in which its movement is facilitated by gas -entering through line I5, and discharges lthrough a funnel-shaped member 28 covered with a suit- :able grid 29 into a vessel 3B, which may be similar in construction to vessel 3. This vesselis also vprovided with internal cooling means represented .by coil 3| and with an internal cyclone 32 hav,-

,ing a dip leg 33 extending below the level 34 of the suspension of uidized s olid maintained in this vessel. Gas leaves the upper .end of this .vessel through a line 35 which passes 'through .-a heat exchanger 36 and thence to storagey or to -`recovery apparatus in whichA itv is ,further processed 4Solid material leaves the bottom of the-vessel is a clean-up vessel in which residual sulfur i s In the embodiment form of Raschig rings, ceramic balls, or the like, Hot air or other vessel through line 4I whichv receives this gas `from a loop 42 which includes'both preheaters 26 and 36 and which receives freshvgas through line 43. Vessel 38 is also provided at various levels with cold air inlets 44. Gas leaves the 4upper end of vessel 38 through line 45 and may be conducted by suitable manipulation of valve 46 through vessel 30 or, by suitable manipulation of valve 41 and valve 48, to line I8. stood that part of this gas may, if desired,.be caused to pass through vessel 3. Residual FezOa is removed from the bottom of vessel 38 through bottom drawoi line 4S. Y v I The rst thing that happens when FeS2 is heated is distillation of half the sulfur. vThe burning of this sulfur is difficult in that it must be completely mixed with air and even then oxidation to SO2 is relatively slow unless the temperature level is very high. Modern sulfur burner design provides for these conditions, but excess air is always required for complete com- .bustion and some S03 formation resultsffln a pyrites roaster much sulfur ox-idaizi'mA ,together It will be under- .130 through a star feeder 31 which discharges the Isolid into the upper portion of a vessel 38. This vsome of the FeS to FeO, thereby providing heat for the distillation of sulfur from FeSz. As a feature of the invention, the duct I0 together With its connecting pipe are suiciently long so that if there is any FeSz left in the solid leaving vessel 3 it will react With the FeO contained in the solid to produce Fes and SO2. Thus, it is fdesirable to conduct the operation in vessel 3 so that some FeO will be formed and to maintain .atleast in the duct Ill a sufliciently high temperature to support the reaction between FeSa .and FeO.- The completion of this reaction in `the ductvprevents the entry of FeS2 into vessel 30' and the sublimation of sulfur from this vessel.

The temperature in vessel 3 should be maintainedlbelow 2000 F. and preferably below 1800 Fpby Isuitable removal of heat by the indirect heat exchanger. The maximum temperature .permissible in this vessel is just below that at which the ore will sinter.

, Sufficient air or other oxygen-containing gas is fed to burner 20 to assure complete oxidation Jofv all distilled sulfur. rThis requires some excess oxygenand introduces some S03 into the off-gas .from-burner 20. High combustion temperatures can be used in burner 20 because there is no solid presentinthis vessel to sinter other than whatevenpacking which may be employed which will be suitably select ed to withstand whatever temperature is maintained. The gas leaving the .burner 20 contains oxygen, SO2, S03 and nitrovif air has been employed. This gas should contain .at least 42% by volume of oxygen and ,preferably more than 5%. The oxygen content ofthis gas can be regulated by controlling the feed of oxygencontaining gas to burner 20.

. The solid passing from vessel 3 to vessel 3D is primarilya mixture of Fes and FeO. Vessel 30 lis als,o .maintained at atemperature below 2000 F. andfpreferably below 1800 F., the top temperature again being regulated by the sintering temperature of the ore. The composition of the solidmixture passing from vessel 3 to vessel 30 controlled by regulating the supply of oxygencontaining gas to vessel 3. The gas recovered from vessel'30 is primarily sulfur dioxide, mixed with nitrogen, if air has been employed.

The solids passing from vessel 30 to vessel 38 Will consist primarily of FeO with a small but 'definite amount of FeS. This content of FeS is deliberately preserved in vessel 30 so as to preclude the formation of S03 in this vessel. Its presence also insures that the off-gas from vessel l30 will be free from oxygen. In vessel 38 the last traces of sulfur are removedwfrom-the solids. To achieve this, strong oxidizing conditions must be maintained, that oxygen in excess of that required to carry the FeO tov Fe/.303.u Therefore, some S03 will be lformed in addition to SO2. The temperature in this-vessel must be high, limited only by the 'sintering temperature ofthe solid. The oxidizing gas and the solids in vessel 38 should pass countercurrent to each other and this may be assured by providing packing in this vessel. 1n order to prevent run-away of temperature in this vessel, cold air may be introduced through the inlets fit at spaced points. In fact, most of the air will be introduced at these spaced points. The quantity of air entering at the bottom is relatively small in amount but should be hot in order to strip all sulfur compounds from the FesOa cinder. The temperature of this air entering' the bottom should be at least 1500" F. and preferably above 1869 the maximum being the fusion point of the cinder.

It will be apparent that the present invention is susceptible to considerable change without sufering any essential change in character. Wherever packing has been recommended in the processing of solids, it will be apparent that trays and bubble caps with dcwncomers can be used as an alternative. Considerable control of the process has been made possible by the various connections from vessel to vessel permitting adjustment oi the composition of the gas passing through any particular vessel. 1t will be understood that the v ssels do not have to have the exact relationships shown so long as the sequence ci operations is suostantially observed. While vessels 3 and have been illustrated as the bottom draxvot? type with internal cyclones, it will be apparent that the operations in these vessels can be so conducted that the solids pass oli overhead to external cyclones or other suitable separators for solids and gases.

The nature and objects or" the present invention having thus been set forth and a specific illustrative embodiment of the same given, what is claimed and desired to be secured by Letters Patent is:

l. A process for roasting' a metal sulfide which liberates sulfur on "ing whicli comprises sus-y pending the s ely divided form in a zene in an upi Y c trearn of oxidizing gas hav a velcc y such to maintain the sulde 'e iuidized. ension, regulating the i 1 Laing cha r'tc-r of the l Zone so as to insure the t of cuide in liberated from said e, reinovi g ated sulfur from ,ation zone in said n of separately removing nely c from said zone, burning removed suliur under controlled conditions to produce a minimum oi SOB, coinn bining the combustion gas so produced with the upflcwing ci oxidizing gas, adjusting the temperature, the oxidizing character' of the and the solid content in roasting Zone so as tc convert substantially all ci the metal sulfide to metal oxide while preserving a minor amount of metal sulfide in said solid suspension and withdrawing from said roasting zone a gas, the sulfur content of which is in the form of SO2, and finely divided solid predominantly composed ci metal oxide and containing a minor amount of metal sulfide.

2. A method according to claim l in which the sulfide is FeSz and the solids passing from the distillation zone to the roasting zone are maintained at an adequate temperature for suiilcient time to permit the FeO contained therein to react with any FeSz contained therein.

3. A method according to claim 1 in which the metal sulfide is pyrites.

4. A method according to claim 3 in which the solid recovered from the roasting zone is subjected to a high temperature treatment with an oxidizing gas to remove the sulfur substantially completely therefrom.

5. A method according to claim 4 in which the clean-up operation is performed by passing the iinely divided solid through a packed zone countercurrent to the oxidizing gas.

6. A method according to claim 5 in which cold air is introduced into said packed zone at different levels thereof in amounts sucient to maintain the temperature within a selected level.

'1. A method according to claim 6 in which the temperature in al1 stages in which solid is present is maintained below the sintering temperature of the solid.

8. In a process for distilling FeSz to produce therefrom a vapor containing principally sulfur with small amounts of SO2, the improvement which comprises feeding solid FeSz in finelydivided form to a bottom portion of a distillation zone, passing an oxygen-containing gas upwardly through said bottom portion of said distillation Zone at a rate such as to maintain the nelydivided solid in the form of a dense fluidized bed having a iveil-deiined upper level, adjusting in said zone the temperature, FeSz content and the amount of the oxygen-containing gas to burn sufficient sulfur contained in the FeSz to supply adequate heat for distilling sulfurv from said FeSz, withdrawing a vapor containing principally sulfur with small amounts of SO2 from an upper end of said distillation Zone and withdrawing a stream of nely-divided solids containing princip'ally Fes from the upper level of the fluidized bed.

WARREN K. LEWIS.

References Cited in the ille of this patent UNTED STATES PATENTS Number Name Date 1,941,592 Bacon et al. Jan. 2, 1934 2,371,619 Hartley Mar. 20, 1945 2,389,133 Brassert et al Nov. 20, 1945 2,393,704 Ogorzaly Jan. 29, 1946 2,409,707 Roetheli Oct. 22, 1946 2,497,940 Hemminger Feb. 2l, 1950 

1. A PROCESS FOR ROASTING A METAL SULFIDE WHICH LIBERATES SULFUR ON HEATING WHICH COMPRISES SUSPENDING THE SULFIDE IN FINELY DIVIDED FORM IN A ZONE IN AN UPFLOWING STREAM OF OXIDIZING GAS HAVING A VELOCITY SUCH AS TO MAINTAIN THE SULFIDE IN A DENSE FLUIDIZED SUSPENSION, REGULATING THE TEMPERATURE AND THE OXIDIZING CHARACTER OF THE UPFLOWING GAS IN SAID ZONE SO AS TO INSURE THE FORMATION OF A MINOR AMOUNT OF METAL OXIDE IN SAID ZONE WHEREBY SULFUR IS LIBERATED FROM SAID SULFIDE, REMOVING SAID LIBERATED SULFUR FROM SAID DISTILLATION ZONE IN SAID STREAM OF GAS, SEPARATELY REMOVING FINELY DIVIDED SOLID FROM SAID ZONE, BURNING SAID REMOVED SULFUR UNDER CONTROLLED CONDITIONS TO PRODUCE A MINIMUM OF SO3, COMBINING THE COMBUSTION GAS SO PRODUCED WITH THE FINELY DIVIDED SOLID REMOVED FROM SAID ZONE, FEEDING THE MIXTURE TO A ROASTING ZONE, MAINTAINING THE FINELY DIVIDED SOLID IN SAID ROASTING ZONE IN THE FORM OF A DENSE, FLUIDIZED MIXTURE IN AN UPFLOWING STREAM OF OXIDIZING GAS, ADJUSTING THE TEMPERATURE, THE OXIDIZING CHARACTER OF THE GAS AND THE SOLID CONTENT IN SAID ROASTING ZONE 